There are applications in which it is desirable to include and use both a telescopic sight and a reflex (“red dot”) sight with a weapon, such as a rifle. However, the problem of installing and efficiently using both a telescopic sight and a reflex sight on the same rifle (or other weapon) has not been entirely solved. Referring to FIG. 1, in a typical configuration, the reflex sight 110 is fixed on the top of the telescopic sight 120. Thus, the eyebox 115 for the reflex sight 110 is located above the eyebox 125 for the telescopic sight 120, as shown in FIG. 1. The eyebox 125 for the telescopic sight 120 is the volume confined by two conuses centered on the optical axis 130 and having a circular exit pupil 140 as a common base. Such a configuration forces an operator to move his/her head up to use the red dot sight and then down to the use magnified telescopic sight again. As a result, the cheek-weld position may not be preserved, and the operator's response may be relatively slow if the combination of sights must be used. Furthermore, raising the head even an inch or so higher to see through the reflex sight can make the operator more vulnerable to actions of an enemy combatant.
Conventional attempts to address these problems have been focused on superimposing imagery from both sights on a common optical axis (typically, the optical axis 130 of the telescopic sight 120). Some examples of such superposition approaches are disclosed in U.S. Pat. No. 6,487,809 and U.S. Pre-Grant Publication No. 2011/0041377. Both of these publications describe complicated optical layouts with additional folding or switchable mirrors or splitters that need to be added to the telescopic sight. There are several disadvantages associated with such layouts. In particular, the fold optics inserted between the eyepiece of the telescopic sight and the operator's eye significantly reduces eye relief. Although it is possible to design a telescopic sight with greater than initially required eye relief, in that case, the field of view in target space will be reduced unless magnification of the telescopic sight is reduced as well. Furthermore, for longer eye reliefs the lens count in the eyepiece is typically higher since correcting for aberrations is more difficult and a field lens must generally be included. U.S. Pre-Grant Publication No. 2011/0041377 discloses an eyepiece having an upright fold, which shortens the length of the sight, but disadvantageously raises the operator's head position above the rifle for both modes of operation (reflex sight mode and telescopic sight mode).
Additionally, in these examples, it is impossible to simultaneously view both the reflex sight channel and the telescopic sight channel, and a switching mechanism is required to toggle between the two modes of operation. Such conventional solutions require many additional optical and mechanical elements, which substantially increases the mass and cost of the system. Furthermore, these solutions are based on very specific design layouts, which cannot be efficiently implemented in combinations of existing off-the-shelf sighting devices.